Microstepping of an unipolar stepping motor

Abstract

High resolution microstepping of an unipolar stepping motor 18 is accomplished by applying from a look-up table the values of the SINE and COSINE of a given angle to the control circuit of a unipolar stepping motor. The difference between the present position and the desired position is calculated and depending upon the magnitude of the difference, the degree of microstepping is determined from four steps per ninety electrical degrees of motor rotation to thirty-two steps. By such selection, the positioning of the output shaft of the motor 18 is smoothly and accurately accomplished.

We claim: 
     
       1. A control system to control the amount of torque output of a stepper motor having windings, said system comprising: means responsive to a control signal for generating at least one torque control signal representing a predetermined amount of motor current control;   means responsive to said one torque control signal for generating an analog signal having a sinusoidal waveshape at a frequency proportional to the rotational speed of the stepper motor;   means responsive to said sinusoidal waveshape signal for providing an amplitude value to said sinusoidal waveshape; and   means responsive to said amplitude sinusoidal waveshape and operable for switching the power to selected ones of the windings of the motor for causing the motor to rotate at a desired value of torque as controlled by said at least one torque control signal.   
     
     
       2. A control system to control the amount of torque output of a stepper motor according to claim 1 wherein said means responsive to a control signal comprises a first voltage divider network for selecting a running torque control current and a second voltage divider network for selecting a holding torque control current. 
     
     
       3. A control system to control the amount of torque output of a stepper motor according to claim 1 wherein said motor is a unipolar stepper motor having at least two phase windings and each phase winding comprises two windings of which one winding from each phase is selected for rotation by another control signal.